1. Field of the Invention
The present invention relates to a liquid crystal display device with a structure in which a liquid crystal panel is sandwiched between a translucent front substrate and a backlight unit, a manufacturing method for the liquid crystal display device, and an electronic apparatus using the liquid crystal display device.
2. Description of the Related Art
A liquid crystal display device is widely used for a display unit of an electronic apparatus such as a laptop personal computer, a cellular phone, a PDA, and an electronic dictionary. The liquid crystal display device includes a non-emissive liquid crystal panel, a backlight provided on a back surface side of the liquid crystal panel for illuminating the same, a front glass provided on a display surface side of the liquid crystal panel, and the like. A method of bonding the liquid crystal panel and the front substrate on the display surface side thereof to each other by using an adhesive is disclosed, for example, in WO 2007/063751 and JP H09-274536 A.
For the purpose of allowing a user to view the liquid crystal display device, an opening portion for exposing the liquid crystal display device therefrom is provided on a cabinet of the electronic apparatus. In the case of placing the liquid crystal display device on the electronic apparatus, it is necessary to assemble a display surface of the liquid crystal display device to the opening portion of the cabinet while performing highly accurate positional alignment for both thereof. This is because an exterior appearance of the display unit is deteriorated when an interval between a parting line of the display unit of the liquid crystal display device and an end portion of the opening portion of the cabinet is widened or narrowed. In the cellular phone taken as an example, a maximum allowable tolerance of an attachment position of the liquid crystal display device onto the cabinet is approximately ±0.4 mm.
FIGS. 13A to 13F illustrate a conventional method of assembling the liquid crystal display device including the backlight and the liquid crystal panel to cabinet of such a portable apparatus. FIG. 13A is a cross-sectional view schematically illustrating a state of preparing a front glass 54 and a liquid crystal panel 53 and attaching both thereof to each other while performing positional alignment therefor. A step difference portion 55 is provided on a display viewed-side surface of the front glass 54, and this step difference portion 55 is formed so as to fit into an opening of an upper cabinet of the portable apparatus. The liquid crystal panel 53 includes a liquid crystal cell 50, an upper polarization plate 51 attached onto a display viewed-side surface thereof, and a lower polarization plate 52 attached onto a back surface thereof, which is opposite to the upper polarization plate 51. The liquid crystal cell 50 has a configuration in which a liquid crystal layer is provided between two glass substrates bonded to each other while interposing a seal member (not shown) therebetween. On an inner surface of one of the two glass substrates, TFTs, pixel electrodes individually connected to the respective TFTs, and the like are formed. On an inner surface of the other substrate, color filters are formed so as to correspond to the respective pixel electrodes.
FIG. 13B is a schematic cross-sectional view illustrating a state where the front glass 54 and the liquid crystal panel 53 are bonded to each other by an optical adhesive 56. Before or after the positional alignment step, the adhesive is applied on the liquid crystal panel 53 or the front glass 54, and the front glass 54 and the liquid crystal panel 53 are positionally aligned with each other and bond to each other. A transparent adhesive of a thermosetting type, a UV-curing or a visible light-curing is used as the optical adhesive 56. The optical adhesive 56 is filled between the liquid crystal panel 53 and the front glass 54, and accordingly, impact resistance and stress resistance of the liquid crystal panel 53 are enhanced.
FIG. 13C is a schematic cross-sectional view illustrating a state of positionally aligning a plastic frame 58 and the liquid crystal panel 53 with each other. The plastic frame 58 includes an LED 61 as a light source, a light guide plate 59 that guides light emitted from the LED 61, a reflection plate 60 provided on a back surface of the light guide plate 59, and an optical film 57 placed on a front surface of the light guide plate 59. Grooves are formed on the front surface of the light guide plate 59, and the liquid crystal panel 53 is irradiated with the light reflected on the grooves. The optical film 57 is provided for efficiently irradiating the liquid crystal panel 53 with the light emitted from the front surface of the light guide plate 59, and for example, the optical film 57 includes a light diffusion plate and a lens film.
In the plastic frame 58, there are provided: a housing portion that houses the reflection plate 60 and the light guide plate 59 on which the optical film 57 is placed; and a step difference 66 for housing the liquid crystal panel 53 in the housing portion. The step difference 66 is formed so that a bottom surface thereof can be flush with a surface of the optical film 57. A light-shielding double-sided adhesive tape 62 is placed on the bottom surface of the step difference 66.
FIG. 13D is a schematic cross-sectional view illustrating a state where the liquid crystal panel 53 and the plastic frame 58 are bonded to each other by the light-shielding double-sided adhesive tape 62. FIG. 13E is a schematic cross-sectional view illustrating a state where the plastic frame 58 is placed on a lower cabinet 64 of the portable apparatus. The lower cabinet 64 and the plastic frame 58 are fixed to each other through an intermediation of a fixing portion 63. For example, pins provided on the lower cabinet 64 are fitted to holes provided in the plastic frame 58.
FIG. 13F is a schematic cross-sectional view illustrating a state where the upper cabinet 65 of the portable apparatus is placed on the step difference portion 55 on the surface of the front glass 54. At this time, gaps δd1 and δd2 are formed between an end portion of the upper cabinet 65 and the step difference portion 55. In the electronic apparatus such as the cellular phone, it is necessary to set those gaps, for example, at ±0.4 mm or less.
In such a manufacturing method as described above, the sum of the gaps δd1 and δd2 is equal to the sum of a positional alignment tolerance a between the front glass 54 and the liquid crystal panel 53 in the step of FIG. 13A, a positional alignment tolerance b between the plastic frame 58 and the liquid crystal panel 53 in the step of FIG. 13C, and a positional alignment tolerance c between the lower cabinet 64 and the plastic frame 58 in the step of FIG. 13E. Therefore, it has become difficult to suppress a gap between the front glass 54 and the upper cabinet 65, for example, within ±0.4 mm, and the exterior appearance of the display unit has been deteriorated. Actually, only by adding the tolerance a and the tolerance b together, the sum thereof has exceeded ±0.4 mm.
Further, though it is probable that the above-mentioned problem may be avoided when the front glass 54 onto which the liquid crystal panel is bonded is bonded onto the upper cabinet 65, the front glass 54 and the liquid crystal panel 53 are subjected to breakage in this case since strength of the upper cabinet 65 is low. Such breakage is caused by the fact that a stress applied to the upper cabinet 65 is directly applied to the front glass 54 and the liquid crystal panel 53. In particular, as illustrated in FIGS. 13A to 13F, in the case of providing the collar-like step difference portion 55 on a peripheral portion of the front glass 54, the step difference portion 55, which is thin, is prone to break. Further, there has been a problem that the liquid crystal display device cannot be thinned in the case of thickening the front glass 54 for the purpose of ensuring strength of the whole device.
Further, in the case of enlarging the front glass 54 more than an outer shape of the liquid crystal panel 53 and fixing the front glass 54 and the lower cabinet 64 to each other by an adhesive, there has been a problem that it becomes difficult to reassemble the liquid crystal panel 53, resulting in that maintenance and the like cannot be performed for the liquid crystal panel.